Image display devices, such as liquid crystal display devices, are disadvantageous in that, when displaying a moving image, boundaries with different display brightness are visually perceived as blurry. Such a deterioration in moving image display performance is due to the following two factors. The first factor is that display elements have a response speed slower than a speed corresponding to one frame cycle of video. A known technology for making up for such a lack of response speed of the display elements is overshoot drive (also referred to as “overdrive”). Overshoot drive is a method for forcibly driving display elements at high speed by applying voltage higher or lower than voltage for achieving a desired gradation level, in accordance with the direction in which the gradation level of a video signal changes (increases or decreases). Overshoot drive is disclosed in, for example, Patent Document 1.
The second factor is that hold-type display elements are used for keeping brightness at an approximately constant level over one frame cycle of video. Concerning this point, Patent Document 2 describes that, in the case of an image display device provided with hold-type display elements, when displaying a moving image, the moving image might appear blurry due to the viewer's following line of sight. To prevent such a moving image blur, the hold time of the display elements is required to be shortened, and specific methods known for this are frame interpolation drive for shortening the length of one frame cycle of video, and time-division gradation drive (pseudo-impulse drive) for approximation to impulse-type light emission as in CRTs. Frame interpolation drive using motion vectors is disclosed in, for example, Patent Document 3, and time-division gradation drive is disclosed in, for example, Patent Document 4.
In addition, Patent Document 5 discloses a drive mode combining frame interpolation drive, in which a frame for compensating for motion of an object image is created and interposed between frames to achieve an increased refresh rate, and overdrive. In this drive mode, an overdrive correction circuit is disposed at the subsequent stage of a frame converter circuit. The frame converter circuit suppresses occurrence of any moving image blur due to the viewer's following line of sight, while the overdrive correction circuit makes up for the lack of response-speed of the liquid crystal display elements, which improves moving image display performance.
[Patent Document 1] Japanese Patent No. 2650479 Publication
[Patent Document 2] Japanese Laid-Open Patent Publication No. 9-325715
[Patent Document 3] Japanese Laid-Open Patent Publication No. 2001-42831
[Patent Document 4] Japanese Laid-Open Patent Publication No. 2005-173573
[Patent Document 5] Japanese Laid-Open Patent Publication No. 2005-91454